1. Field of the Invention
The present invention relates to a data transfer unit, and more specifically to a data transfer unit interposed between devices for executing data exchange by a handshaking process based on a signal level. The invention also pertains to a method of supplying power to the data transfer unit.
2. Description of the Related Art
Known data transfer units include one interposed between a personal computer and a peripheral device such as a printer for conversion of parallel data to serial data or vice versa and one connecting a plurality of devices by a daisy chain for serial data communications.
Data conversion and transmission requires power of a predetermined voltage for activating general purpose synchronous/non-synchronous transmission ICs (for example, UART) and other logic circuits or for driving line drivers and receivers. The required power is generated in a power supply circuit incorporated in a data transfer unit, which includes a battery or is connected to a commercial power source.
In a general structure, the data transfer unit as well as communication devices connected to the data transfer unit receive power from the commercial power source, thus requiring many receptacles. The conventional data transfer unit requiring an outlet for the commercial power source can not be placed at an arbitrary position even when a computer and a printer are driven by an internal battery. The data transfer unit having an internal battery has other problems; that is, consuming labor and time for charging and replacing the battery, and making the data transfer unit undesirably bulky.